My application Ser. No. 039,702, now U.S. Pat. No. 4,739,561, described a level indicator for use in the installation of prehung doors. However, each one of these indicators, while it solved the problem of freeing a carpenter's hands for other jobs than holding the level, was limited in its application to a door of a given thickness, and there remains a need for a level indicator that can be readily and removably atttached, not only to doors of varied thickness, but to other wooden structures in a manner that will free a caprenter's hands to work on them. My above-mentioned patent and the prior art patents cited therein are incorporated herein by reference but none of them bear any suggestion of the novel and useful structure to be described.